As an aluminum oxycarbide, the following two types: Al2OC and Al4O4C, have been known. In particular, Al4O4C is stable at high temperatures and excellent in oxidation resistant, corrosion resistance and thermal shock resistance, so that it is expected as a refractory or ceramic material, or a raw material therefor. Especially, Al4O4C is expected as a raw material for a carbon-containing refractory material, such as an alumina-carbon based refractory material or a magnesia-carbon based refractory material, used as a refractory material for use with molten metal such as molten iron or steel.
As a production method for Al4O4C, a sintering process of heat-treating a carbon-raw material and an alumina-raw material in a burning furnace, or a melting process of melting a carbon-raw material and an alumina-raw material in an arc furnace, are being studied, although they have not been put to practical use.
For example, as disclosed in the following Non-Patent Document 1, it has been experimentally confirmed that Al4O4C is formed by heat-treating powdery alumina and powdery graphite in an argon atmosphere. This production method comprises: adding ethanol to alumina having a mean particle diameter of 0.1 μm and graphite reagent having a particle size of 45 μm or less; mixing them in an agate mortar; drying the obtained mixture; putting the dried mixture in powder form (2 g) into a graphite crucible; setting the crucible in an electric furnace; forming a vacuum within the electric furnace; and then burning the mixture at 1700° C. while supplying argon gas into the electric furnace.
The Non-Patent Document 1 says that, in a test carried out under conditions that a mole ratio C/Al2O3 is set to 0.5, 1.5, 2 and 3, when C/Al2O3=1.5, an amount of formation of Al4O4C was maximized without forming Al2OC and Al4C3, and therefore the best blend ratio for synthesis of Al4O4C is considered to be 1.5. However, it is mentioned that pure Al4O4C free of Al2O3 and graphite was not obtained. Further, a produced composition had a particle diameter of about 10 to 100 μm.
In the production method disclosed in the Non-Patent Document 1, it is assumed that the formation of Al4O4C from a carbon-raw material and an alumina-raw material is progressed according to chemical reactions expressed by the following Formulas (1) to (3):2Al2O3(s)+3C(s)=Al4O4C(s)+2CO(g)  (1)2Al2O3(s)+4CO(g)=Al4O4C(s)+3CO2(g)  (2)CO(g)+C(g)=2CO(g)  (3)
However, it is mentioned that, when C/Al2O3 becomes greater than 1.5, Al4C3 is also formed according to the following Formulas (4) and (5), and the formation of Al4C3 according to the following Formulas (4) and (5) is facilitated along with an increase in heating time.Al4O4C(s)+8CO(g)=Al4C3(S)+6CO2(g)  (4)Al4O4C(s)+6C(s)=Al4C3(S)+4CO2(g)  (5)
The following Patent Document 1 discloses a method of producing an aluminum oxycarbide composition using an arc furnace. In inventive examples disclosed in the Patent Document 1, various coarse grain consisting primarily of alumina-aluminum oxycarbide and having total carbon contents of 0.8 mass %, 1.11 mass %, 1.76 mass % and 2.13 mass %, respectively, are obtained by adding carbon to 100 mass parts of Bayer process alumina, in amounts of 2.5 mass parts, 5.0 mass parts, 10.0 mass parts and 12.5 mass parts, and melting the obtained mixture in an arc furnace. In a comparative example where carbon is added to 100 mass parts of Bayer process alumina, in an amount of 15 mass parts, a refractory aggregate having a total carbon content of 3.10 mass % is obtained. The Patent Document 1 says that a refractory aggregate having a total carbon content of 3.0 mass % or more is not suitable as a refractory raw material, because the aggregate is likely to form aluminum carbide (Al4C3) which easily reacts with water. It is also mentioned that, when the aggregate was applied to a refractory material, hot bending strength was significantly and undesirably deteriorated.
The Non-Patent Document 2 discloses a technique of producing an aluminum oxycarbide composition by a method similar to that in the Patent Document 1, wherein the aluminum oxycarbide composition has an apparent porosity of 0.3 to 1.2%, an apparent specific gravity of 3.24 to 3.87, and an carbon content rate of 0.83 to 3.14 mass %. It is mentioned that a sample prepared in the Non-Patent Document 2 contains Al4C3, because it can react with water to generate methane gas.
The following Patent Document 2 discloses a carbon-containing brick containing aluminum oxycarbide, and the following Patent Document 3 discloses a monolithic refractory material containing aluminum oxycarbide. In the Patent Documents 2 and 3, it is mentioned that aluminum oxycarbide is produced by heating a mixture of alumina and carbon under an argon atmosphere or the like at 1400° C. or more.